CPD Quiz: Anatomy and Physiology of the Central Nervous System
Educational Courses, Conferences & Events
Anatomy and Physiology of the Central Nervous System The nervous system is highly organised, and one of the most complicated systems of the human body. Its primary function is concerned with the association and integration of various bodily processes and the reactions and adjustments of the organism to its environment.
Divisions of the Nervous System
Figure 1: Divisions between Central and Peripheral Nervous Systems
Although the nervous system functions as a unified whole, structures and functions of the nervous system have been divided to facilitate understanding. Structurally, the nervous system is divided into the central and the peripheral parts. The central nervous system (CNS) consists of the brain and spinal cord, enclosed within the protective cranial vault and vertebrae, respectively. The peripheral nervous system is composed of the cranial 30
Content Provided by AusmedOnline.com
nerves, which project from the brain and pass through foramina (openings) in the skull, and the spinal nerves, which pass through intervertebral foramina of the vertebrae.
?
Quick Question: The central nervous system is made up of the brain and spinal cord.
True / False?
CPD Quiz: Anatomy and Physiology of the Central Nervous System
Functional Unit of the Nervous System
?
Quick Question: The basic unit of the nervous system is:
a. Axon b. Neuron c. Neuroglia/Glial cells
Blood Supply to the Brain and Spinal Cord The brain receives approximately 20% of the cardiac output, or 800 – 1000 ml of blood flow per minute. The brain derives its arterial supply from two systems: the internal carotid and the vertebral arteries. The internal carotid arteries supply a proportionately greater amount of blood flow. They take their origin from the common carotid arteries, enter the cranium though the base of skull. They divide into anterior and middle cerebral arteries. The vertebral arteries, Content Provided by AusmedOnline.com
31
Educational Courses, Conferences & Events
The two basic types of cells that make up nervous tissue are neurons and supporting cells called neuroglia or glial cells. The neuron is the primary cell of the nervous system. Neurons process sensory information, integrate signals from other bodily systems, generate higher cognitive processes and initiate responses to maintain homeostasis. Neuroglia or glial cells support the neurons of CNS. They make up approximately half of the total brain and spinal cord volume and are five to ten times more numerous than neurons. These cells form contacts between the neurons allowing for rapid transport of nutrients and metabolites. A neuron has three components: a cell body, dendrites and an axon. The neuronal processes (dendrites and axons) vary in size from micrometre to several metres long. The shapes and complexity of neurons can vary considerably. Neurons carry electrical messages to and from the brain and to the rest of the body. The cell body contains the cell nucleus and a concentration of cellular organelles in the cytoplasm. The nucleus is spherical and contains a well-marked nucleolus. Unique to the nerve cell cytoplasm are Nissl bodies, which are vesicles located near the nucleus, and are involved with protein synthesis. The cell body is the site of the normal metabolic reactions that allow the cell to remain viable. Neurotransmitters synthesised within the cell body are transported to the axon terminus where they are released as chemical messages across the synapse. The dendrites are extensions of the cell body that carry nerve impulses towards the cell body. The axon is a long projection from the cell body that carries impulses away for the cell body. The junction of the axon and
cell body is called axon hillock. The axon may be long, up to a metre in length in humans or short, depending upon the neuron’s position and function. A typical neuron has only one axon, which may be covered with a segmented layer of lipid material called myelin sheath. Myelin acts as an insulator that allows ions to flow between segments rather than along the entire length of the membrane, resulting in increased velocity. The cell membranes of the axon transmit neural signals via changes in action potentials that sweep down the membrane. Axon terminals have knob-like swellings at the very end called synaptic knobs or end boutons. Each synaptic knob communicates with a dendrite or cell body of another neuron, the point of contact being a synapse. At the axon terminus, neurotransmitters are released into the synaptic gap. Through synaptic gaps, a typical neuron may interconnect with thousands of other neurons.
Educational Courses, Conferences & Events
CPD Quiz: Anatomy and Physiology of the Central Nervous System
Figure 2: Blood Supply to the Brain and Spinal Cord
posteriorly, originate as a branch of subclavian arteries, and enter the cranium through foramen of magnum. They join at the junction of the pons and medulla oblongata to form the basilar artery. The basilar artery divides to form paired posterior cerebral arteries. These three major paired arteries perfuse the cerebellum and brain stem: the posterior inferior cerebellar artery from the vertebral artery; and the anterior inferior cerebellar and superior cerebellar arteries from the basilar artery. At the base of the brain, the carotid and vertebrobasilar arteries form a circle of communicating arteries known as the circle of Willis. Because the carotid and vertebrobasilar arteries form a circle, if one of the main
arteries is occluded, the distal smaller arteries that it supplies can receive blood from the other arteries (collateral circulation). This provides collateral blood supply and can often preserve the cerebral perfusion well enough to avoid major tissue infarct in the event of a stroke. The spinal cord derives its blood supply from the branches of vertebral arteries and from branches from various regions of aorta.
?
Quick question: 1. What is the circle of Willis and what vessels constitute this circle? 2. What is the functional significance of the circle of Willis?
Content Provided by AusmedOnline.com © Copyright AusmedOnline 2010 Complete your answers online to find out the correct results. Visit: www.ausmed.com.au/ quick-quiz now! Wanting to learn more? Listen to a lecture on ‘How to Prevent Pressure Sores in Frail and Elderly People’ for free at AusmedOnline. This lecture will earn 21 minutes towards your CPD. 32
DOCUMENTING YOUR CPDs Ausmed’s Free CPD Organiser will assist you with your CPD documentation and quickly take you through the correct process of recording. The CPD Organiser is available at: www.AusmedOnline.com